Wide-angle lens system with corrected lateral aberration

ABSTRACT

The present invention relates to an extreme wide angle lens system having an angle of coverage of 180* which comprises eleven lens elements including an interchangeable filter. This improved extreme wide angle lens system with sufficient light intensity has a relative aperture of up to F/2.8 with a comparatively small number of compact lens elements and the lateral aberration as well as various aberrations thereof are greatly corrected.

3 589 798 K L/ o 1 o X 4/ F D I [72] Inventor ToshL ences Citedsakfli-shi-hpan UNlTED STATES PATENTS i f 3: 1969 2.969.7l3 l/l96l Mukai.1 350/214 3.132.199 5/1964 Zimmermann m1 350/214 Patented June 29, 1971[73] Assignee Minolta Camera KabushikiKaisha FOREIGN PATENTSOsaka,.]apan 0,475,134 11/1937 Great Britain .1 350/205 [32] PriomyPrimary Examiner David Schonberg [33] Japan Ass/51am Examiner- Paul A.Sacher 1 [9328/68 AI/orney-Watson, Cole. Grindle & Watson {54]WIDE-ANGLE LENS SYSTEM WITH CORRECTED I F L S B T ABSTRACT: The presentinvention relates to an extreme 3 "wing wide angle lens system having anangle of coverage of [S2] U.S.Cl 350/198, which comprises eleven lenselements including an in- 350/205. 350/214 terchangeable filter. Thisimproved extreme wide angle lens [5] Int. Cl G02bl3/00, system withsufficient light intensity has a relative aperture of G02b 9/00 up toF/2.8 with a comparatively small number of compact [50] Field ofSelrch350/198, lens elements and the lateral aberration as well as various205, 214 aberrations thereofare greatly corrected.

r l? r6 r9 n2 n6 n9 l'Zl r1 I f3 1 Y8 1 l P/ l 1 l on 163 J d|1 d1s19dl9 PATENTED JUN29 I971 SHEET 1 [IF 3 o m w w mmd d8 7 'G G d INVENTURTosh Nolou 0 mm BY mange, G kfle wax ATTORNEYS WIDE-ANGLE LENS SYSTEMWITH CORRECTED LATERAL ABERRATION BACKGROUND OF THE INVENTION There weresome extreme wide lens systems with an angle coverage of up to l80,l-Iowever, such prior lens systems are not very useful in practicebecause the lens structure has low light intensity owing to acomparatively small relative aperture which results from variousproblems such as difficulty in correcting the lateral chromaticaberration, the strong residual monochromatic aberration, and the largedimension of lens elements and so forth. I

SUMMARY OF THE INVENTION The prime object of the present invention is toprovide an extreme wide-angle lens system with a relative aperture of upto F/2.8 by eliminating the said defects of prior wide-angle lenssystems after correcting various aberrations including the lateralchromatic aberration, most difficult to remove, to the same degree asthat of usual lens systems.

The second object of the present invention is to provide an extremewide-angle lens system which is applicable to a 35 mm. single lensreflex camera with no fear of hindering the rotating motion of areflecting mirror by making the back focal distance over twice the focallength.

The third object of the present invention is to provide an extremewide-angle lens system by which a field angle of 180 can be mapped on adiagonal in the photographing plane.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the structure of thefirst embodiment of the present invention of an extreme wide lenssystem,

FIG. 2 shows the structure of the second embodiment,

FIG. 3 shows the structure of the third embodiment, FIG. 4 shows curvesof the aberrations in the first embodiment,

FIG. 5 shows curves of the aberrations in the second embodiment, and

FIG. 6 shows curves of the aberrations in the third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1 through FIG.3, an extreme wide-angle lens system of thepresent invention comprisesll lens elements including an interchangeable filter G6. Both the firstlens element G1 and the second lens element G2 are divergent meniscuslenses which are disposed with the convex surfaces facing the objectside, the third lens element G3 and the fourth lens element G4 are adivergent lens and a biconvex lens, respectively, which are used eitheras a cemented doublet or as individual lens elements, the fifth lenselement G5 is a convergent lens which is disposed with the convexsurface directing to the object side, the sixth lens element G6 is afilter, the seventh lens element G7 and the eighth lens element G8 are aconvergent meniscus lens and a divergent meniscus lens, respectively,which are used either as a cemented doublet or as individual lenselements and disposed with the convex surfaces facing to the image side,the ninth lens element G9 and the 10th lens element G10 composing acemented doublet are a divergent lens and a biconvex lens, respectively,and the llth lens element G11 is a convergent lens. The said extremewide lens system satisfies the following conditions.

where I r r, the radii of curvature of the refracting surfaces numberedin sequence from the object side,

d,. d the axial separations between consecutive refracting surfaces,

N N the refractive indices of lens elements,

V,, V z the Abbe numbers oflens elements,

f, the focal length of the whole system.

In the above-mentioned conditions and the embodiments to be mentionedbelow, the numbering of surfaces is carried out in sequence aftersplitting the doublet into individual lens elements when the third lenselement G3 and the fourth lens element G4 as well as the seventh lenselement G7 and the eighth lens element G8 are cemented to be doublets.

I The sixth lens element G6 is an interchangeable filter which can beremoved from the system when unnecessary, or positioned behind the lastlens element G11. Usually, a stop is positioned between the fifthelement G5 and the seventh lens element G7.

Characteristics and functions of the structure of the lens system of thepresent invention will be described in the followmg.

The first three lens elements are positioned in the front portion of thesystem in order not to allow an excessive angle of inclination of lightpenciles introduced at half field angle of or so and to obtain a longback focal distance. In order to reduce the considerable lateralchromatic aberration produced therein as much as possible, it isnecessary to dispose two convergent lens elements, the fourth lenselement G4 and the fifth lens element G5, between the said threedivergent lens elements and the stop which contribute effectively to thecorrection, and at the same time to require condition (a) on selectingAbbe numbers.

If the condition is not fulfilled, satisfactory correction cannot beattained by any selection of Abbe numbers of the lens elements in therearward portion of the system.

The condition (b) on the achromatism is necessary for five lens elementsin the rearward portion from the stop in order to EMBODIMENT I 1, 1:2.8,Field angle 2w=180, Back focal distance=2.281

Radil of Axial Refractive Abb curvature separations lndlces numbersdi=0.13 N =1.6204 Vi=60.3 rz=1.1846

d =0.12 N =LGZO4 vt=60.3 Tt=1.0494

d =0.4779 rs=2.6996

lis=0.1 N =1.6204 a=60.3 ri=6.4885

da=0.04 rr=4.5007

d7=0.4151 Ni=L6645 4=35-9 3.0057

d5=0-009 ru=2.1925

d9=0.4722 Ns=1.7330 s= 8-2 rw=347222 il m 11=0.0933 Nt=1.5994 Vt=40.8

dir=0.2983 m= -1.6272

ia=0.3413 N7=L6214 V =6L2 11 0.6060

du=0 T s= 0.6060

dis=0.148l N3=L7330 Va=28.2 m= 1.3364

I diu=0.009 T 7= -9.5039

d 7=0.085 NB=I-.7400 Vo=37.5 m=1.5755

d1a=0.415 Niu=L5688 V1o=56.0 T1o= 1.9997

d19=0.009 Tzo=3.301fi dgg=0.265 Nu=1.5168 1=64.2 'm= 4.I338

correct the longitudinal chromatic aberration produced excessively bythe selection of Abbe numbers in the front portion from the stop asmentioned above. and to attain a further correction for the residuallateral chromatic aberrations Since the lens system covers a half fieldangle as wide as of 90. the condition (c) gives an effective measure toobtain an appropriate value of the Petzval sum by eliminating a negativetendency of the said sum produced by the intensive divergent lenselements in the front portion of the lens systems and to eliminate thespherical aberration produced by the convergent elements. If the saidcondition is not fulfilled. at least the correction for the sphericalaberration becomes inevitably unsatisfactory. ln order to reduce themagnitude of the spherical aberration and the astigmatism as much aspossible and to eliminate coma produced in the front portion from thestop. while keeping a long back focal distance. it is necessary todispose five lens elements in the rearward portion from the stop. andthe condition (d) is required for curvature of the said lens elements.

Three embodiments of the present invention based on the above-mentionedconditions are described in the following. where d= means a cementeddoublet.

A filter G6 is sometimes removed or positioned behind the last lenselement in practical cases.

EMBODIMENT II FIG. 1; no. 2. and FIG. 3 show the structures of lenssystems in the first, the second. and the third embodiments.respectively. 7

FIG. 4, FIG. 5, and FIG. 6 show the behavior of the correctedaberrations in the first. the second, and the third embodiments.respectively, where each aberration is proved to be well corrected inspite of the aperture up to F/2.8 at half field angle of 90", whilekeeping along back focal distance.

Moreover, the lens system comprises a comparatively small number of lenselements and is compact so that it is very useful in practice.

l. A wide angle lens system having a focal length of 1.0. a focalaperture of l:2.8, a field angle of l80 and ll elements successivelymounted from the object side comprising;

first and second lenses of the divergent meniscus type each having itsconvex surface facing the object,

a third lens of the divergent type,

a fourth lens of the biconvex type,

a fifth lens of the convergent type having its convex surface facing theobject.

a sixth element is a filter,

a seventh lens of the convergent meniscus lens type having 1 its convexsurface facing the image,

an eighth lens of the divergent meniscus type having its convex surfacefacing the image.

a ninth lens of the divergent type,

a lOth lens ofthe biconvex type.

an 1 lth lens ofthe convergent type.

wherein the indicated lens elements have the following characteristics,wherein r,, r,...r,, are defined as the radii ofcurvature oftherefracting surfaces as indicated in FIG. I, d,, 4 nd,, are defined asthe axial separations between consecutive refracting surfaces asindicated in FIG. I,

N N,....V,, are defined as the refractive indices of the respective lenselements. and

V,, V uzl are the Abbe numbers of the respective lens elements, and

the back focal distance is 2.28,

2 A wide-angle lens system having a focal length of L0, a focal apertureof l:2.8, a field angle of l80 and ll elements successively mounted fromthe object side comprising;

first and second lenses of the divergent meniscus type each having itsconvex surface facing the object,

a third lens of the divergent type,

a fourth lens of the biconvex type,

a fifth lens of the convergent type having its convex surface facing theobject,

a sixth element is a filter,

a seventh lens of the convergent meniscus lens type having its convexsurface facing the image,

an eighth lens of the divergent meniscus type having its convex surfacefacing the image,

a ninth lens ofthe divergent type,

a th lens of the biconvex type,

an 1 lth lens of the convergent type,

wherein the indicated lens elements have the following characteristics,

i Radiiol l Axial Refractive Abb curvature separations indices numbers[1 :11.13 N;=l.ti204 \'i=60.3 r2=l..1870

di=o.4909 73:2.478

ds=0.l2 Nz=1.6176 1:52.? T =Lo464 d4=0.4784 l =-2.7105 i ds=0.1 INa=1.6205 \';\=60.3 rs=1.2057

d7=0A701 N =1.T495 \]=34.9 =--3.Z290

do=0.4746 NFL7330 =28.2 Till d u=0.1 I rn== I an=0.o9sa l N =L599-tvi=4os m== di =0.3381 l N7=L62l4 V1=6L2 r =0.6079

tin-=0 ri =-0.6079 l di5=0.148l l N5=LT330 V5=28.2 f g=l.3408 fdii=0.009 ri1=8.0756

d17=0.085 I NFL i400 3:315 T1 ==L6141 dis=0.395 Ni =L5688 \'i =56.Orip-3.0450 t d 9=0.009 I 20=3.3647 1 1120 0.285 .\'n=l.5168 "11 64.2Tzi=-3.5348

za=4.03aa I I wherein r,, r ...r are defined as the radii of curvatureofthe refracting surfaces as indicated in FIG. 2,

d,, d,...d are defined as the axial separations between consecutiverefracting surfaces as indicated in FIG. 2,

N,, N ...N are defined as the refractive indices of the respective lenselements, and

V,, V WV are the Abbe numbers of the respective lens elements, and

the back focal distance is 2.27.

3. A wide-angle lens system having a focal length of L0, a focalaperture of 122.8, a field angle of l and l l elements successivelymounted from the object side comprising:

first and second lenses of the divergent meniscus type each having itsconvex surface facing the object, athird lens of the divergent type,

a fourth lens of the biconvex type,

a fifth lens of the convergent type having its convex surface facing theobject,

a sixth element is a filter,

a seventh lens of the convergent meniscus lens type having its convexsurface facing the image,

an eighth lens of the divergent meniscus type having its convex surfacefacing the image,

a ninth lens of the divergent type,

a 10th lens of the biconvex type,

an I lth lens of the convergent type,

wherein the indicated lens elements have the following characteristics,

Radii 01 Axial Refractive Abb curvature separations indices numbersdi=0.13 Ni=1.6000 Vi=64.1 7'2=l.154.2

d2=0.5029 Ta=2.4737

(1 :0.12 N 2:1.6204 Vr-GOJ! H=L0536 =-4.2637 d3=0.009 Tg=2.5309

(1 :0.5000 N s=1.7847 V =26.7 T 0=10.6383

dio=0.1 n=

dn=0.0929 Ne=1.5994 Vs=40.8

di2=0.3007 m 1.5145

d1 =02629 N7=L6426 7 58.1 r =0.7029

d1 =0.06 ris=0.6344

dis=0.15 N5=L7557 73:27.2 l' g= 1.4149

, dit=0.009 r 5.1808

d17=0.085 N =L74OO 0:37.5 T g=1.6218

di =0.42 Nio=1.6891 V 10 61.2 T 9=1.8597

d =0.009 rap- .4936

120 0. Nn=1.6000 Vndail ri 2.0515

1. A wide angle lens system having a focal length of 1.0, a focalaperture of 1:2.8, a field angle of 180* and 11 elements successivelymounted from the object side comprising; first and second lenses of thedivergent meniscus type each having its convex surface facing theobject, a third lens of the divergent type, a fourth lens of thebiconvex type, a fifth lens of the convergent type having its convexsurface facing the object, a sixth element is a filter, a seventh lensof the convergent meniscus lens type having its convex surface facingthe image, an eighth lens of the divergent meniscus type having itsconvex surface facing the image, a ninth lens of the divergent type, a10th lens of the biconvex type, an 11th lens of the convergent type,wherein the indicated lens elements have the following characteristics,2. A wide-angle lens system having a focal length of 1.0, a focalaperture of 1:2.8, a field angle of 180* and 11 elements successivelymounted from the object side comprising; first and second lenses of thedivergent meniscus type each having its convex surface facing theobject, a third lens of the divergent type, a fourth lens of thebiconvex type, a fifth lens of the convergent type having its convexsurface facing the object, a sixth element is a filter, a seventh lensof the convergent meniscus lens type having its convex surface facingthe image, an eighth lens of the divergent meniscus type having itsconvex surface facing the image, a ninth lens of the divergent type, a10th lens of the biconvex type, an 11th lens of the convergent type,wherein the indicated lens elements have the following characteristics,3. A wide-angle lens system having a focal length of 1.0, a focalaperture of 1:2.8, a field angle of 180* and 11 elements successivelymounted from the object side comprising: first and second lenses of thedivergent meniscus type each having its convex surface facing theobject, a third lens of the divergent type, a fourth lens of thebiconvex type, a fifth lens of the convergent type having its convexsurface facing the object, a sixth element Is a filter, a seventh lensof the convergent meniscus lens type having its convex surface facingthe image, an eighth lens of the divergent meniscus type having itsconvex surface facing the image, a ninth lens of the divergent type, a10th lens of the biconvex type, an 11th lens of the convergent type,wherein the indicated lens elements have the following characteristics,